17 Jun
2013
17 Jun
'13
6:54 p.m.
I've
experienced this, trying to use a USB serial adapter in place of an
ASR-33 to serve up an imaged paper tape on a PDP-8/e. It does not work.
It's an interesting question as to why this is a problem. :-)
Is it because of baud (bit) rate or an incompatibility? If the former, most baud rate generators won't
generate 110 unless specific
crystals/divisors are chosen. Otherwise they'll start at 300.
If the latter, I've found that some USB serial adapters aren't friendly to
classic
gear. I haven't thrown an analyzer between them to figure it out. I've found
some that seem to work most often (Belkin springs to mind...still doesn't
support 110 though).
I have made some strange serial port experiences - under Linux. Can't speak for
the Windows world.
1. I see no general incompatibility between real or USB serial ports on a PC and
a PDP8. The RIM and BIN loaders can cope with at least 19200 baud. Probably even
more. Without any handshake. And KL8E for example works at 19200 without any
problem. You don't have to stick with 110...
2. I am a Linux user. And I have encountered one big problem with Linux and
serial ports: If I send a file down the port via cat, the transfer stops
immediately when cat closes the port. The data in the FIFO or anywhere between
the application and the UART seem to be lost.
I have not always seen those problems. On my current Linux 3.4.5 box I can cat
and everything works fine.
One fix back when I had problems on my notebook was to disable the FIFO in the
8250 driver.
Another one is something like doing a
(cat <file>; sleep 0.1) > /dev/ttyXX
Then You open a subshell which has its output connected to the port. And the
delay makes it possible to drain all buffers before the port is closed.
BTW with Omni-USB all these problems are UNKNOWN :-)
Kind regards
Philipp
--
Dipl.-Inf. (FH) Philipp Hachtmann
Buchdruck, Bleisatz, Spezialit?ten
Alemannstr. 21, D-30165 Hannover
Tel. 0511/3522222, Mobil 0171/2632239
Fax. 0511/3500439
hachti at hachti.de
www.tiegeldruck.de
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